Strain measuring and load controlling apparatus



Nov. 12, 1946.,

STRAIN N. H. ROY EI'AL 2,411,139 MEASURING AND LOAD CONTROLLING APPARATUS Filed Nov. l8, 1945 ZSheets-Sheet 1 i I'll V W 1 L T 2i lll I I I )I all 10a. '2o 11 4. 14 32 33 Mb 34 {8 (10 a 31 m 2 1o 36 1' i 4ob 8 L6 a o bl, 22 4 16.2 u i? iLa'HD INVENTORS NerguS HRoy Jose hLl BLsesL A Z'TORNEY Nov. 12, 1946. NHROYETAL v 2,411,139

STRAIN MEASURING AND LOAD CONTROLLING APPARATUS Filed Nov. 18,1943 ZSheets-Sheet 2 INVENTOPJ NergusHRoy J05 h L. Bisesi,

A 'I'TORNE V Patented Nov. 12, 1946 STRAIN MEASURING Ann LOAD CONTROLLING APPARATUS Nereus H. Roy, Glenbrook, Conn.,

Bisesi, Floral Park, N. Y. Company, Philadelphia,

Pennsylvania and Joseph L.

, asslgnors to The Budd Pa., a corporation of Application November-18, 1943, Serial No. 510,110

8 Claims. 1

This invention relates to strain measuring and load controlling apparatus and has for an object the provision of improvements in this art.

One of the particular objects of the invention is to provide apparatus for measuring strains and controlling loads, which includes a strain measuring device which is incorporated in and becomes a part of the member under stress.

Another object is to provide a complete selfcontained strain measuring device of a convenient mechanical arrangement which facilitates loading the resistance units which form the strain sensitive elements.

Another object is to provide strain measuring and load control apparatus which is adapted without alteration to register either tension or compression strains and to control the load in accordance with either.

Another object is to provide a compression type strain sensitive device which is so mounted and arranged that both compression and tension strains are always transmitted to the strain sensitive element as relative or differential compression efiects.

Another object is to provide a self-contained preloaded strain sensitive unit which can be installed by simple mechanical connections as an integral part of various load carrying members.

Another object is to provide a centrally disposed strain sensitive element to which ardai strain effects are transmitted in an arziai direction.

-Another object is to provide such a device which is not effected by vibration in use.

In the measurement of strains in structures and elements of structures, it has been common practice in the past to employ, among other types, a carbon'resistor type of gage temporarily attached externally to the structure by means of screws or clamps; Due to the size and weight of these gages, it was often inadvisable to superimpose their relatively great weight on the structure. Moreover, the drilling of holes in the structure or member under test was objectionable in that the use of the member for its in- Fig. 4 is a wiring diagram of one arrangement of the apparatus.

For purposes oi" illustration the strain responsive and load controlling apparatus of the present invention is shown in association with airplane wing flap control means and the strain measuring unit I0 is shown to be mounted between the spaced ends we of the push-pull tube or rod 5 which operates the wing flaps, the pre-assembled strain responsive unit thus becoming an integral part of the load-carrying member. The motor M as indicated in Figure 4 has power connection to gear means 6 through which the push-pull or control rod 5 is axially reciprocated.

The container or enclosure lb of the strain measuring unit i0 is shown to be a round tube of a size to fit the ends of the push-pull tube but it is evident that for other uses it may have other shapes. Within the container Nib there are mounted two carbon pile resistance units Ha, iib. These carbon pile units are secured in the tube under pro-compression and are so arranged that when the push-pull tube its, and the container iii?) are loaded in tension the carbon pile unit i It is subjected to an increase in compression, and unit Ha is subjected to a decrease in compression; and when the tubes Illa and 10b are loaded in compression, unit lib is subjected to a decrease in compression and unit I la is sub-- jected to an increase in compression; a differential between the compression in the two carbon pile units is produced in either case, and this differential is a measure of the strain in the test member. In the present arrangement the tube may not be subject to compression at any time, but only a variation in tension; however, that causes a variation or diiferential between the compression in the two carbon pile units which serves the desired purpose.

The mounting means for the carbon pile units in the container lob comprises a series of four plates l2, l3, l4 and I 5 and two sets of connecting rods l6 and IT. The end plates l2 and I5 are firmly secured to the tube on the inside at a distance apart as by screws l8; and the intermediate plates l3 and i l move axially within the tubular container in response to 1engthening' or shortening thereof.

The left fixed plate i2 and the right floating plate Id are secured together by the set of rods I6; and the right fixed plate l and the left floating plate l3 are rigidly secured together by the set of rods l1. Each floating plate I3, or id; is cut away to allow the unattached set of rods [5 or I! to pass freely thereby and may be generally Y or triangular shaped with three spider arms as shown in Fig. 2.

The floating plate I3 is disposed between the two carbon pile units I la and Nb, hence the set as the floating plate It is disposed beyond both pile units and its set of rods l6 embraces both pile units Ila, lib. The pile units and their plates are ,therefore held together as a self-contained unit by the set of rods l6.

Initial compression on the pileunits lla, llb may be regulated by adjustment screws 20, ll threaded in the plates I2 and M respectively, the adjustment screws being held in fixed position by locknuts 22.

Fig. 3 shows the details of one of the carbon pile units. It may consist of a number of carbon plates or annular rings 25, insulating plates 28 near each end, and end plates 29 with conical pointed thrust projections an. Electrical conductors 3!, 32, 33 and 3 3 are secured to metal washers 26 at the terminal carbon plates of the two pile units (Fig. 1). Two of the conductors, one from each unit, may be connected to a common outside lead while the other two conductors pass out separately. They emerge in a threewire cable 535 from a junction box at clamped to the rod id.

Referring to the wiring diagram of Fig. 4, the carbon pile units lla, ill) in the tube are shown in circuit with other apparatus to provide active control of operating parts, as for example the wing flaps heretofore referred to. A grounded control box 62, which is preferably mounted to resist shocks, is indicated in dotted outline and includes two resistancesv 56 and 5? connected in series with the carbon pile resistances Ma and lib. These four resistances lla, llb, 5i and 56 constitute the four resistances of a Wheatstone bridge circuit, current being supplied at points 53 and 59 and the output of the bridge being measured between points at and b l.

In order to place this bridge circuit under the control of the pilot, panel gang switches A and B are provided, each switch having four contacts numbered Al, A2, A3 and A 3 for A and El, B2, B3 and B6 for B. The pivot of the switch arm 52 of switch A is connected to the positive pole of a battery, preferably the storage battery of the airplane, with a voltage commonly of between 20 and 25 volts, the negative pole of the battery being grounded. The pivot of the switch arm 63 of the switch B is connected to bridge point Ell.

' Contacts Al and A6 are connected to bridge point 59. Contact Bl is connected through a temperature responsive variable resistor lid and the coil 65 ofa sensitive relay Rl to the bridge point El. Contact Ed is connected through resistor 65 to contact Bl.

'It is thus apparent that with contacts Al and BI engaged by the mechanically connected switch arms 62 and 63, power is suppliedto the bridge circuit at points 58 and 59 and variation in bridge balance voltage is applied at bridge points till and l of rods I1 embraces only the pile unit I lb, wheregreater. rod tension may be permitted.

BI to vary the current through the relay coil 65.

The motor M which is grounded at 69 on the negative side of the armature has dual field circuit wires to the contacts 6'! and 68 of a relay R2 through the limit switches l0 and ll. Each of the switches has a spring-closed contact arm which is adapted to be opened by the push-pull rod operating screw member ill when'moved by the motor to the limiting position. The movable arm 12 of the relay R2 is pivoted at l3 and connected to the positive side of the battery. Movement of the relayarm between points 67 and 68 reverses the direction of rotation of the motor.

, The relay R2 includes coils id and I5 connected in series with the junction point grounded, the outer ends of the coils being connected to the contacts 16 and ll of relay Rl. The arm or blade 19 of the relay RI is biased toward the contact ll by a spring at, the anchorage 8| of the spring being adjustable to vary the spring tension. The pivot of the arm 79 is connected to bridge point 59. In addition to relay coil it, switch contact A2 is also connected to the contact it of relay Rl. In operation, when the airplane rests on the ground the switches A and B are positioned at the "off" points A3 and B3. At take-off the switches are moved to contacts Al, Bl to energize the bridge circuit. The push-pull rod being unstrained and the bridge balanced, the relay contacts, H and 68 are closed and the flaps are lowered by the motor M until stopped by openin the lower limit switch ll.

With the flaps down, the plane takes ofi and as air speed increase the tension of the flap opcrating rod It increases. This separates plates l2 and is within the tubular rod and increases the compression on thecarbon pile unit l lb. The compression on carbon pile unit lla is decreased.

The bridge is unbalanced and at a predeter mined point where the coil 65 overcomes the spring so the contact E5 of relay Rl is closed and the motor is energized to raisethe flaps. When the tension pressure is relieved sufilciently by raising the flaps the prior connections are reestablished and the motor again lowers the flaps. This alternate flap movement continues until the airplane is well in the air.

The pilot then moves the yoked switches to contacts A2, B2 which takes the carbon pile units out of circuit and raises the flaps to their upper limiting position where they stay.

For landing, the same general situation as for take-off prevails except that a higher speed and The switches are turned to contacts Ad, Eli and a resistance 56 is cut in circuit with relay coil and more unbalance between the carbon pile units l la, l lb is required to unbalance the bridge circuit enough to raise the flaps than the case of take-oil.

With the same arrangement, should the push= pull rod be loaded in compression instead of tension the distance between the plates l2 and it will shorten and the compression on carbon pile unit No will be increasedwhile the compression on the carbon pile lib will decrease to give a differential effect in the bridge circuit and thus operates the controls.

It will thus be seen that the invention provides a very simple and effective strain control device in general and a number of specific improvements in detail. The carbon pile units are held together in compression as a unit in the tubular container and the container with the pile units is a complete entity which can be built and tested oi the prior art and the scope of the snbioined claims.

What is claimed is:

1. in load controlling apparatus in combina= tion, a load=taking member, a pair oi carbon pile electrical resistance units mounted therein, and connections between said member and. said units for difierentially affecting said, units with change in length of said member, said connections comprising spaced plates secured to said member, floating plates between said fixed plates,

and rod sets connected each to a different floating plate and a different fixed plate.

2. in load controlling apparatus in combination, a load-taking member, a pair of carbon pile electrical resistance units mounted therein, and connections between saiclmember and said units for differentially affecting said units with change in length of said member, said connections comprising two spaced plates fixed to said member, two floating plates between said fixed. plates, one floating plate being disposed between units and the other between a unit and one of said fixed plates, and rod sets connected each to a difierent fixed plate and a different floating plate.

3. In load. controlling apparatus in combination, a load-taking member, a pair of carbon pile electrical resistance units mounted therein, and connections between said member and said units for differentially affecting said units with change in length of said member, said connec= tions comprising two spaced plates nixed to said member, two floating plates between sainfixed plates, one floating plate being disposed between units and the other between a unit and one or" said fixed plates, and rod sets connected each to a fixed plate and a floating plate and extending by the other floating plate. s

e. In load controlling apparatus in combina= tion, a, tubular load-taking member, a of carbon pile electrical resistance units mounted therein in axial alignment with each other, and connections between said member and i for differentially ailecting said units r in length of salcl member at points nail to said units, said connections comprising two spaced, plates fixed to said member, two floating plates between said fared plates, one floating plate being disposed between units and the other between a unit and one of said fixed plates, and rod sets connected each to a clifierent fixed plate and a different floating plate.

5. In load controlling apparatus, a unitary self contained strain responsive unit adapted to be inserted as a linlr of a load transmitting member comprising a link member adapted to be connected at each end to the load. transmitting member for load transmission, and at least two variable electrical resistance elements mounted on said link member in axial series alignment with each other, the adjoining ends of two of said ele ments being attached to a first common point on said load member and the corresponding outer ends oi said two elements being attached. to a second point on said load member displaced from said first point.

6. Apparatus as set iorth in claim 5 further characterized by the fact that said variable resistance element comprises a pair oi" differential compression carbon pile units formed as a selfcontained unit with two rod sets and four supporting plates including two end plates with the end plates only attached to said container.

7. In load controlling apparatus, a unitary self contained strain responsive unit adapted to be inserted as a link of a load transmitting memoer comprising two resistance elements variable in resistance with degree of strain and. connected in physical series, the outer ends of said series elements being connected to a common first point on said load member and the inner ends of the elements being connected to a common second;

point on said load member displaced from the first point.

8. in load controlling apparatus, a unitary self contained strain responsive unit adapted to be inserted as a link of a load transmitting member comprising two resistance elements variable resistance with degree of pressure and connected in physical series, the outer ends of said series elements being connected to a common first point on saidload member adjacent one outer element end and the inner ends of the elements being connected to a common second point on said load member displaced from the first point and adjacent the other outer element end.

NEREUS ROY. JCSEPI-Z BISESI. 

